Good point about running out of battery.

I picked up a $10 timer from Radio Shack. I set it for 12 minutes just before I launch. When 12 is up, I approach for landing, bring her in dead stick most of the time, just because I like to, then slide her into the grass. I have kept it up til the motor dies several times and typically that has been 14-15 minutes.

Setting a timer is a very good habit to get into especially as you become experienced and tend to venture a little higher and a little farther out, then a lot higher and a lot farther out.

You don't want to lose the motor when you are 100 feet up, 500 feet out which might be 200 feet into a wooded area and flying against the wind. It can get messy!